Nitride semiconductor light emitting devices such as a blue light emitting diode (LED), a laser diode or the like, using nitride semiconductor have been lately in practical use. The semiconductor light emitting device using nitride semiconductor and emitting blue light is formed by laminating, for example on a sapphire substrate, in order by MOCVD method, a low temperature buffer layer made of GaN or the like, an n-type layer made of GaN or the like, an active layer (light emitting layer) made of material, for example InGaN based (which means that a ratio of In to Ga can be varied variously and the same applies hereinafter) compound semiconductor, which has a smaller band gap energy than that of the n-type layer and decides a wavelength of emitted light and a p-type layer made of GaN or the like. And a p-side electrode is formed over a surface thereof interposing a light transmitting conductive layer, and an n-side electrode is formed on a surface of the n-type layer exposed by etching a part of the semiconductor lamination portion. Additionally, a semiconductor layer having still larger band gap energy such as AlGaN based (which means that a ratio of Al to Ga can be varied variously and the same applies hereinafter) compound or the like may be employed on an active layer side of the n-type layer and the p-type layer in order to increase an effect of carrier confinement.
When the nitride semiconductor layers are laminated by the MOCVD method, since Mg which is introduced as an acceptor of a p-type layer is apt to be combined with H because raw material gas contains hydrogen of an alkyl group, carrier gas is hydrogen and NH3 which is raw gas of nitrogen contains hydrogen, then the Mg is taken in the semiconductor layers in a form of Mg—H, while combining with H. When Mg and H exist combined in a semiconductor layer, the Mg is inactivated and can not function as an acceptor. Therefore, an annealing treatment is generally carried out in an atmosphere of a temperature of 400° C. or more and not containing hydrogen, in the prior art, and the Mg as an acceptor is activated by separating off Mg and H by heat and dispersing the H out of the nitride semiconductor layer (cf. for example PATENT DOCUMENT 1).
In this case, a laser annealing treatment carried out by irradiating a laser beam has been employed for the annealing (cf. for example PATENT DOCUMENT 2). When annealing is carried out by the laser annealing method, since a temperature only in the vicinity of a p-type layer can be raised without raising a temperature of whole semiconductor lamination portion, there is an advantage such that diffusion of dopants into an active layer or the like is easily inhibited. Although a laser beam of a short wavelength is required to be used from necessity of raising a temperature of a nitride semiconductor layer since GaN has a high absorption coefficient at a short wavelength corresponding to a band gap energy Eg or more because GaN is direct transition semiconductor, a depth of entering of a laser beam into the nitride semiconductor layer becomes small, and it becomes difficult to activate a thick p-type nitride semiconductor layer.    PATENT DOCUMENT 1: Japanese Patent Application Laid-Open No. HEI8-51235    PATENT DOCUMENT 2: Japanese Patent Application Laid-Open No. 2002-289550